Rivers

• Drainage basin


  The area that is drained by a river and any tributaries
• Watershed


  The boundary of the drainage basin
• Components of a natural system

  • Outputs
  • Stores
  • Flows
• Evaporation


  The change in state of water from liquid to gas
• Evapotranspiration


  Compromised of evaporation and transpiration
• River discharge


  The volume of water passing through a cross-sectional point of the river at any one point in time, measured in Cubic Metres Per Second (Cumecs)
• Interception


  Water (e.g. precipitation) that is intercepted by plants' branches and leaves before reaching the ground
• Soil Water


  Water that is stored in the upper levels of the soil, which is utilised by plants
• Surface Water


  Water stored in puddles, ponds, lakes etc
• Groundwater


  Water that is stored in the pore spaces of rock or lower soil
• Channel Storage


  Water that is stored in a river's channel
• Types of flows


  • Above ground flows
  • Below ground flows
• Throughfall


  Water flows from leaves and foliage onto the ground
• Stemflow


  Intercepted water stored on plants and trees flows down a stem onto the ground
• Overland flow


  Water flows above the ground, as sheetflow or in rills
• Channel flow


  Water that moves through established channels, like streams or rivers
• Infiltration


  The movement of water from above ground into the soil
• Percolation


  Water flows from the ground or soil into porous rock or rock fractures
• Throughflow


  Water flows through the soil and into streams or rivers
• Groundwater Flow


  Water flows through permeable rocks, below the water table, and may also flow as springs
• Baseflow


  The level of channel flow when there is no overland flow (i.e. when no precipitation has fallen)
• Underground water makes up a large amount of the Earth's water stores, in fact it accounts for around 30% of all the Earth's freshwater
• Aquifers


  Underground water stores
• Water table


  The level at which the pore spaces and fractures in the ground become saturated
• Groundwater Recharge


  1. Precipitation infiltrating the ground until it reaches groundwater

  2. Surface water bodies (such as lakes and rivers) seeping into groundwater stores
• Spring


  A natural outlet of groundwater
• Hydrograph


  A graph that shows how river discharge changes over time
• Components of a storm hydrograph

  • Discharge
  • Rising Limb
  • Falling Limb
  • Lag Time
  • Baseflow
  • Stormflow
  • Bankfull Discharge
• Flashy hydrograph


  • Short lag time
  • Steep rising and falling limb
  • Higher flood risk
  • High peak discharge
• Subdued hydrograph


  • Long lag time
  • Gradually rising and falling limb
  • Lower flood risk
  • Low peak discharge
• Annual hydrograph


  Shows how discharge changes over a year
• Subdued Hydrograph


  Long lag time and low peak discharge
• Features of Flashy and Subdued Hydrographs

  • Flashy:
  • Short lag time
  • Steep rising and falling limb
  • Higher flood risk
  • High peak discharge

  Subdued:

  • Long lag time
  • Gradually rising and falling limb
  • Lower flood risk
  • Low peak discharge
• Annual hydrographs show how discharge changes over a year. The discharge is usually an average, such as a daily or weekly average. Annual hydrographs allow different trends of a river to be seen, such as seasonal variations.
• Hydrographs vary in different ways (as seen by flashy/subdued hydrographs, and the variation in discharge on an annual hydrograph). These variations are influenced by a number of factors, mainly concerned with the climate the river is in, and the drainage basin the river is part of.
• Precipitation


  Variations affect hydrographs. Overall, more precipitation will lead to a flashier storm hydrograph, and will also create higher levels of discharge on an annual hydrograph.
• Storm events influence hydrographs

  Fast and heavy rainfall falling in short periods of time leads to not enough time for the water to infiltrate, and instead it flows into the channel. Bankfull discharge is reached quickly and any discharge above that line on the hydrograph flows outside the river channel.
• Type of precipitation

  If water falls as snow, it can be stored as surface water for longer, affecting the lag time.
• Temperature


  Has a direct relationship with evaporation. When temperatures are higher, water particles have more energy, meaning they are more likely to evaporate. This leads to lower overall discharge.
• Antecedent moisture


  The pre-existing level of moisture within soil before precipitation. The level of moisture in the soil affects the amount of infiltration, which therefore affects hydrographs.